Amid questions over how Edward Snowden gained access to critical data, experts cite the technical limits and far-reaching oversight within the agency.

The Maryland-based National Security Agency is under scrutiny after Edward… (Saul Loeb / AFP/Getty Images )

WASHINGTON — Security experts questioned Monday how, three years after Army Pfc. Bradley Manning downloaded a trove of secret material, low-level computer specialist Edward Snowden was able to copy documents that are far more sensitive and walk them out of his National Security Agency workplace in Hawaii.

After Manning released hundreds of thousands of classified documents — for which he is now being court-martialed — government officials vowed to curtail the broad access to intelligence that came into being after the Sept. 11 attacks. But Snowden appeared to have access to far more sensitive secrets, including the first order from the Foreign Intelligence Surveillance Court to be leaked in its 35-year history.

"I do think it raises questions about how good our controls are on our system," said Stewart Baker, a former general counsel for the NSA. "Because anything that he was able to move to a thumb drive to exfiltrate could also be exfiltrated by Russian or Chinese hackers."

Snowden is almost certainly facing serious charges related to espionage and the conveyance of national defense information, said a former senior FBI official who would not be quoted by name because of the sensitive subject matter.

The FBI is interviewing Snowden's family members, as it would in any similar investigation, to "gain insight into his motivation and mind-set, to include communications, emails, phone calls, writings," and also to determine whether he was communicating with a foreign power or had been recruited by an intelligence service, the former FBI official said. He said Snowden's choice of Hong Kong as a refuge raises questions about possible cooperation with China.

After acquiring a government security clearance when he worked for the CIA, Snowden moved into a contractor job with his clearance still active. Most recently, before decamping for Hong Kong, he was working for government contractor Booz Allen Hamilton in Hawaii.

"The question that a lot of people are asking is why did the CIA grant him a clearance," said a former senior government official who demanded anonymity because he was not authorized to speak about the case.

Snowden described himself to the Guardian newspaper in London, which first published details of a massive telephone-data collection program, as a computer systems administrator who performed technical rather than operational functions. His job, however, gave him access to a wide swath of secrets.

Baker pointed out that computer network maintenance jobs "are self-taught jobs in some respects, and the guy is clearly an impressive autodidact."

But analysts said that Snowden seems to have greatly exaggerated the amount of information available to him and people like him.

Any NSA analyst "at any time can target anyone, any selector, anywhere," Snowden told the Guardian. "I, sitting at my desk, certainly had the authorities to wiretap anyone from you or your accountant to a federal judge to even the president if I had a personal email."

Robert Deitz, a former top lawyer at the NSA and CIA, called the claim a "complete and utter" falsehood.

"First of all it's illegal," he said. "There is enormous oversight. They have keystroke auditing. There are, from time to time, cases in which some analyst is [angry] at his ex-wife and looks at the wrong thing and he is caught and fired," he said.

NSA analysts who have the authority to query databases of metadata such as phone records — or Internet content, such as emails, videos or chat logs — are subject to stringent internal supervision and also the external oversight of the foreign surveillance court, former NSA officials said.

"It's actually very difficult to do your job," said a former senior NSA operator, who also declined be quoted by name because of the sensitive nature of the case. "There are all these checks that don't allow you to move agilely enough."

For example, the former operator said, he had go through an arduous process to obtain FISA court permission to gather Internet data on a foreign nuclear weapons proliferator living abroad because some of the data was passing through U.S. wires.

"When he's saying he could just put any phone number in and look at phone calls, it just doesn't work that way," he said. " It's absurd. There are technical limits, and then there are people who review these sorts of queries."

He added, "Let's say I have your email address. In order to get that approved, you would have to go through a number of wickets. Some technical, some human. An individual analyst can't just say, 'Oh, I found this email address or phone number.' It's not simple to do it on any level, even for purely foreign purposes."

The former senior government official said that as a computer expert, Snowden could have gained access on the NSA computer network to some of the documents he purportedly leaked. But other documents he claims that he provided to the Guardian and the Washington Post, such as the FISA order, are in theory supposed to be kept more tightly held, he said.

One of the issues investigators will be examining is "what access was he granted and what access did he gain" himself in order to obtain the documents, the former official said.